1. Field of the Invention
The present invention relates to an image scanning apparatus that can automatically determine a size of an original document placed on an original document platen and to a method of determining a size of an original document.
2. Description of the Related Art
In an image scanning apparatus such as a copier and a facsimile machine, when scanning image information of an original document placed on an original document platen, an original document platen cover is closed to press the original document, and then the image information is scanned by a flatbed scanner. The flatbed scanner includes an image scanning sensor such as a Charge Coupled Device (CCD) line sensor or the like, and acquires the image information of the entire original document by moving a scanning portion at a constant speed.
Before scanning the image information of the entire original document, it may be necessary to detect a size of the original document, and various mechanisms are known for automatically detecting the size of the original document. For example, a first conventional image scanning apparatus lights a light source immediately before a platen cover is closed, scans waveform data (image information) with a line sensor, and thus detects a size of an original document in a main scanning direction from the waveform data.
A second conventional image scanning apparatus presses an original document by a press sheet having a diffuse reflectance that is higher than that of a white reference plate, and scans brightness data of the press sheet including the original document in the above-described state.
When detecting the size of the original document from the waveform data, it is preferable to detect the size at the earliest possible timing in a process of closing the platen cover. However, when acquiring the waveform data when an opening/closing angle of the platen cover is relatively great, an edge of the original document may not be detected or may be mistakenly detected due to “disturbing light.” Disturbing light is an outside source of light, such as indoor light or sunlight, other than light that is used for determining document size or document scanning, and which may disturb accurate document size determination or document scanning.
As in the first image scanning apparatus, when acquiring the waveform data immediately before the platen cover is closed, a size detection sensor in a sub scanning direction of the original document may respond to a pressing surface of the platen cover, possibly leading to an erroneous detection. Moreover, an edge of the original document is not limited to white but may be various colors such as black and gray. Accordingly, depending on a density of the edge of the original document, the edge of the original document may not be detected or may be mistakenly detected.
In the second image scanning apparatus, the size of the original document is determined by scanning the brightness data of the press sheet including the original document after the platen cover is closed. Accordingly, in the case where all the color or almost all the color of the original document along a scan line is white, the edge of the original document may be mistakenly detected.